The use of dental floss is recommended by virtually all dental health practitioners According to the Council on Dental Therapeutics, dental flossing has been shown to be 80% effective in removing interdental plaque, yet only about 12% of the United States population use floss regularly. Many consumers find floss to be inconvenient, hard to hold, hard to get between teeth and have problems with the floss fraying and shredding during use. For this reason, floss producers have been seeking ways of making floss easier and more pleasant to use. Unfortunately, most solutions are not particularly efficient and add significant cost to the product.
One approach that has resulted in reduced fraying and shredding is the use of polytetrafluoroethylene (PTFE) monofilament yarn for floss. Unfortunately, PTFE yarns are approximately ten times more expensive than the traditional nylon yarn and its use more than doubles the cost of the floss to the consumer. PTFE floss products are supplied by Gore, Colgate and the Personal Products Company division of McNEIL-PPC, Inc. These products have set the standard for fray and shred resistance. However, PTFE monofilament floss is difficult to provide with adequate flavor because it does not have adequate surface area to carry the flavors. PTFE floss is difficult for the consumer to hold while flossing because it has a low coefficient of friction, and many consumers feel it does not clean between teeth as well as conventional multifilament floss.
A second approach is described in U.S. Pat. No. 5,226,435 and U.S. Pat. No. 5,357,990 assigned to Gillette Canada, Inc. These patents describe a dual-coated, flattened or shaped product using conventional multi-filament yarn. According to these patents, the yarn is initially coated with a first wax and is subsequently coated with a second wax, the melting temperature of the first wax being higher than the melting temperature of the second wax. The first wax coating binds the filaments of the multi-filament yarn together after which it is flattened or shaped. The second coating contains flavor and/or other additives. This product is significantly less expensive than PTFE, but has more flavor impact than some commercially available PTFE monofilament floss. While floss made according to these patents passes more easily between teeth than some other conventional flosses, for many consumers, this product is too thin, does not have the flavor impact of conventional flosses and does not provide the fray/shred resistance of PTFE.
European Patent Application EP 0 790 040 A1 to Ranir/DCP Corp. discloses a dental floss made from high molecular weight polyethylene yarn having a coefficient of friction of less than about 0.2 and a tensile modulus of about 200 to about 2500 grams per denier. The yarn is preferably coated with a coating material such as a wax. The Ranir patent asserts that the properties of the floss disclosed therein are expected to translate into easier insertion between teeth and less fraying and shredding. Our tests show that the force required to pass floss believed to manufactured in accordance with the '040 patent between teeth is equivalent to most conventional multifilament flosses and higher than PTFE monofilament floss. Further, our tests show that this product frays and shreds more than PTFE products. This floss is also significantly more expensive than conventional nylon multi-filament floss since it comprises a yarn whose cost is about 6 times the cost of nylon yarn.
By "shredding," we mean the breaking of yarn filaments of the floss during use. By "fraying," we mean the permanent separation of adjacent filaments of the floss during use. Frayed floss often results in the filaments becoming stuck between teeth, especially between teeth containing restorations.
Manufacturers of prior art flosses have twisted the substrate yarn to prevent fraying. It is well known that fraying of a yarn generally increases as the number of twists per inch decreases (see for example, "Oral Hygiene Products and Practice," by Morton Pader, Marcel Deckker, Inc., New York, 1988, pages 181-182), While adding twist does indeed reduce fraying, increasing the twist of the floss increases its diameter, thereby making it more difficult to pass between teeth.
Bragg (U.S. Pat. No. 4,151,851) discloses that adding twist to floss "causes the strand to be substantially cylindrical in cross section with the strand having a width much larger than individual filaments. Such floss may be difficult to insert between a person's teeth when the teeth fit closely against each other. It has been found that if the twist is removed so that the individual filaments lie parallel to the longitudinal axis of the strand, . . . , the strand will be flat or ribbon shaped, as shown, with a thickness that may be on the order of 0.0005". Such a flat strand, when present edgewise will be easier to insert between closely fitting teeth." While Bragg discloses that a flat tape-like floss will pass more easily between teeth, he does not teach how to prevent shredding or fraying of the yarn.
In light of the continued deficiencies in prior art floss, it is an object of the invention to provide a floss with improved fray and shred resistance.
It is another object of the invention to provide a floss which slides easily between teeth while providing the user with the perception of effectively cleaning between the teeth.
It is another object of the invention to provide a floss which is easy to handle and is gentle on the fingers and gums.
It is another object of the invention to provide a floss that can carry large amounts of flavors and/or other additives.
It is a further object of the invention to provide a floss with all of the above-mentioned attributes.